Can I use plain yogurt as an antifungal cream on vagina lips?

Is Safe. Should be safe to do. Does it work? I don't know. But worth a try.
You can. There are some studies that suggest that eating yogurt or using it topically can help in the treatment of vaginal yeast infections. The current antifungal medications are universally found to be more effective, and there are several that are available without a prescription. If those measures don't work, see your gynecologist to be sure that it is indeed a yeast infection.